During operation of a machine, if a foreign object enters the working region of a machine operating part, it interferes with the machine operating part, possibly impeding normal operation or even damaging the machine. Conventionally, various methods have been employed to avoid such an inconvenience.
For example, a collision of a machine operating part with a foreign object is detected by using a touch sensor mounted to the outer surface of the machine operating part. The provision of the sensor, however, entails an increase in the cost of the machine, and it is not possible to detect a collision of the machine operating part with a foreign object occurring outside the operable region of the sensor. In those types of machines in which the machine operating parts thereof are driven by servomotors, it is known to detect a collision of a machine operating part with a foreign object by detecting an increase in the driving current for the corresponding servomotor in excess of a predetermined discrimination current value caused by the collision. However, there is a considerable period of time from the occurrence of the collision until the servomotor driving current actually reaches the discrimination value. Therefore, a delay in the collision detection is inevitable and thus the collision can bring about greater damage due to the delay. Other types of machines, e.g., industrial robots are known in which a collision discriminating process is executed by a built-in computer in accordance with a sensor output or the detected value of the servomotor driving current. Namely, in machines of this type, the collision discriminating process is executed by the computer which is used for controlling the robot; in other words, both the collision discriminating process and the robot control are carried out by the same computer. The robot control, however, involves a variety of complicated data processings, and accordingly, execution periods of the control process and the collision discriminating process of the computer become inevitably long. Consequently, time passes until the collision discriminating process is completed after an occurrence of collision, thus further increasing the delay in the collision detection.